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Effect of Lanthanide Additives
Mikito KITAYAMA, Kiyoshi HIRAO, Motohiro TORIYAMA, Shuzo KANZAKI
1999 Volume 107 Issue 1251 Pages
995-1000
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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Alpha-Si
3N
4 powder mixed with SiO
2 and Ln
2O
3 (Ln=La, Gd or Yb) was heat-treated at 1750-1900°C. After removing the glassy phase, the morphologies of β-Si
3N
4 crystals were quantitatively analyzed. The aspect ratios of β-Si
3N
4 crystals doped with different lanthanide oxides increased in the order of La
2O
3>Gd
2O
3>Yb
2O
3 at high annealing temperatures. The anisotropic Ostwald ripening model successfully simulated grain growth behaviors of β-Si
3N
4 with different lanthanide additives, and suggested that the observed difference in grain growth behaviors be due to the change in the reaction rate at the (100) interface between the β-Si
3N
4 crystal and the Ln-Si-O-N liquid phase.
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Yuichi SAWAI, Yuji IWAMOTO, Sachiko OKUZAKI, Yoshiyuki YASUTOMI, Koich ...
1999 Volume 107 Issue 1251 Pages
1001-1006
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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Chemically modified polycarbosilane containing organofluoric groups, PCOCF, was synthesized and used as a compaction binder for SiC ceramics. The powder fluidity and the powder packing property were evaluated by measuring angle of repose, tap density, green density and pore size distribution of both the binder coated powders and the compacts. The PCOCF coated SiC powder showed improved fluidity and packing property, owing to the organofluoric side chains of PCOCF. Thus, the PCOCF coating was found to be the most effective among other binders to lubricate the SiC particles, which results in a higher compaction under the same loading conditions. The compact of PCOCF coated SiC powder contains only homogeneously dispersed small pores, and therefore, the mechanical strength of the sintered body can be improved, the scatter in bending strength values being also significantly reduced due to the PCOCF coating.
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Mamoru AIZAWA, F. Scott HOWELL, Kiyoshi ITATANI
1999 Volume 107 Issue 1251 Pages
1007-1011
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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Strontiumapatite (Sr
10(PO
4)
6(OH)
2; SrAp) powder was prepared by the ultrasonic spray-pyrolysis technique and was characterized. Three kinds of starting solutions with a Sr/P molar ratio of 1.67 were prepared by mixing Sr(NO
3)
2, (NH
4)
2HPO
4 and HNO
3; the concentrations of Sr
2+ and PO
43- were in the ranges of 0.10 to 0.50mol·dm
-3 and 0.06 to 0.30mol·dm
-3, respectively. These solutions were sprayed into the heating zone to prepare the SrAp powders. The heating zone was composed of two electric furnaces; the lower furnace served for the evaporation of the solvent from the droplets (400°C), the upper furnace for the pyrolysis of the precipitated metal salts (850°C). Easily sinterable SrAp powder was prepared by spray-pyrolysis from a starting solution containing 0.10mol·dm
-3 of Sr
2+ and 0.06mol·dm
-3 of PO
43-. The resulting powder was composed of spherical and solid particles filled with fine primary particles. This SrAp powder was thermally stable up to 1200°C. Even without calcination and grinding operations, the relative densities of the compacts fired at 1200°C for 5h attained maxima of -96%. The microstructure of the sintered compacts appeared to be uniform; the average grain size was -2μm.
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Vesselin DIMITROV, Takayuki KOMATSU
1999 Volume 107 Issue 1251 Pages
1012-1018
Published: November 01, 1999
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Interaction parameter
A proposed in Yamashita-Kurosawa's theory has been calculated for numerous single component oxides. It has been assumed that in the case of simple oxides it represents, through the electronic polarizabilities of the ionic pair the interaction between oxide ion and the corresponding cation due to overlapping of their outermost electronic orbitals to form a chemical bond. It has been proposed that the parameter
A is closely related to the polarizability of the oxide ion as well as the optical basicity of the oxides. The obtained almost linear distribution of the basicity in respect to Yamashita-Kurosawa's parameter
A could be used as an optical basicity scale for simple oxides. Systematic decrease of the O1s and outermost cation binding energies with decreasing interaction parameter has been established. It has been associated with decreased charge overlapping between electronic shells of the oxide ion and cation, which relates to large electronic polarizabilities of both cation and oxide ion and increased optical basicity, that is increased ionicity of the chemical bond.
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Katsuya KUDAKA, Kiyokata IIZUMI, Takeshi SASAKI
1999 Volume 107 Issue 1251 Pages
1019-1024
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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TiC and TiB
2 powders were mechanochemically synthesized from powder mixtures of elemental Ti-C (atomic ratio 1:1) and Ti-B (1:2) in 34h 45min and 15h 10min, respectively, in a planetary ball mill using tungsten carbide balls. TiN powder was also mechanically synthesized from titanium powder for 60h in a high-energy horizontal rotary ball mill (steel balls) equipped with a nitrogen gas flow system. The as-milled mixed powders have been characterized as a function of the milling time by means of X-ray diffraction, scanning electron microscopy and X-ray fluorescence spectroscopy. The reaction processes for TiC and TiB
2 formation were initiated by mechanically induced solid-state diffusion in the induction period when carbon or boron atoms diffused into titanium, and a small amount of TiC or TiB
2 was formed by solid-state diffusion until a mechanically induced self-propagating reaction occurred. The reaction process for TiN formation proceeded via the surface reaction of titanium particles with molecular nitrogen and the mechanically induced solid-state diffusion of nitrogen atoms into titanium. The lattice parameters obtained for TiC, TiB
2 and TiN agree with previously reported measurements.
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Katsuyuki MATSUNAGA, Yuji IWAMOTO, Craig A. J. FISHER, Hideaki MATSUBA ...
1999 Volume 107 Issue 1251 Pages
1025-1031
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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Molecular dynamics (MD) simulations based on Tersoff interatomic potentials have been carried out for amorphous silicon carbonitride (Si-C-N) ceramics. Short-range atomic arrangements and self-diffusion behavior in Si-C-N are investigated. In the Si-C-N amorphous network with homogeneously distributed carbon atoms, silicon atoms are bonded to both nitrogen and carbon atoms, forming mixed tetrahedra of Si(C, N)
4. The average coordination number of C to Si is nearly three, which is larger than that of N to Si. The calculated self-diffusion coefficient of Si decreases with increasing carbon content in the Si-C-N systems. This indicates that C atoms play a role in reducing atomic diffusivities in Si-C-N at high temperatures, which may explain the observed thermal stability of Si-C-N amorphous ceramics.
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Kazuyuki SUZUKI, Wataru SAKAMOTO, Toshinobu YOGO, Shin-ichi HIRANO
1999 Volume 107 Issue 1251 Pages
1032-1036
Published: November 01, 1999
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Patterned KTa
0.50Nb
0.50O
3 (KTN50) thin films with a (100) preferred orientation were successfully crystallized at 700°C on MgO (100) substrates. Both benzoylacetone (BZAC)-modified KTN precursor and 2-ethoxyethanol (EGMEE)-modified KTN precursor films showed charge-transfer UV absorption. The decrease in CH and CO absorptions in the IR spectra for the EGMEE-modified precursor was more rapid than that in the BZAC-modified precursor. Perovskite KTN films with a prominent (100) orientation crystallized at 700°C on MgO (100) substrates from both systems. However, the epitaxy of KTN films from the EGMEE-modified precursor combined with UV treatment was better than that from the BZAC-modified precursor. The optical transmittance of KTN films from the EGMEE-modified precursor showed a better interference fringe than that from the BZAC-modified precursor. UV-treated KTN films on Pt(100)/MgO(100) substrates, which were derived from the EGMEE-modified precursor, revealed the highest dielectric constant and the lowest loss. Patterned KTN films from the EGMEE-modified precursor had a smooth and pore-free surface, according to scanning electron microscopy (SEM) observation.
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Cong WANG, Yoshihiro ABE, Toshihiro KASUGA, Masayuki NOGAMI
1999 Volume 107 Issue 1251 Pages
1037-1040
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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Sol-gel derived P
2O
5-SiO
2 glasses were studied and a remarkable improvement in protonic conduction was observed by increasing the P
2O
5 content. This was attributed to (1) the variation in glass structure including the reduction of the degree of cross-linking skeleton and the increase of specific surface area of glass due to the non-bridging oxygen (P=O) in P-O tetrahedron, (2) the formation of stronger hydrogen bond between hydroxyl group and P=O group as well as hydroxyl group and, (3) the p-π resonance effect in O
(3-t)PO(OH)
t unit.
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Hitoshi TAIMATSU, Taroh ATSUMI, Tadashi OKANIWA, Koji KODAMA
1999 Volume 107 Issue 1251 Pages
1041-1045
Published: November 01, 1999
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The mechanism of solid-state reaction between B
4C and Ti powders has been examined in the temperature range between 1000°C and 1300°C. In the early stage of the reaction, TiB and nonstoichiometric TiC
0.58 in equilibrium with C-saturated Ti were formed from B
4C and Ti; then TiB
2 and TiC
x containing higher amounts of C were formed from TiB, TiC
0.58 and remaining B
4C until the reaction ceased at an
x-value of 0.69. This reaction path was not changed basically in the temperature range examined although the reaction rate was increased with temperature. Every product grain consisted of a TiC
x core and a TiB
2 layer around the core. This suggests that B hardly migrates in products and the reaction proceeds mainly by inward C diffusion and outward Ti diffusion through the products.
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Influence of the Size of Buffer Domain on Plasticity
Shuji KAWAI, Hideki ISHIDA, Yasuo SHIBASAKI, Kiichi ODA
1999 Volume 107 Issue 1251 Pages
1046-1049
Published: November 01, 1999
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The plasticity of ceramic dough is controlled by the deformation of the buffer domains, that consist of aggregates or gel. Influence of the variation of each buffer domain on the plasticity of alumina dough was investigated by changing the size of the non-water-soluble plasticizer. The diameter of the plasticizer strongly influenced the formation of the buffer domain. It was found that a plasticizer gel size in the range 10-1000μm well performs as buffer domain and its deformation generates plasticity. Plasticizer smaller than 10μm cannot be a suitable buffer domain, resulting in a lower plasticity of the dough.
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Influence of the Deformability of Buffer Domain on Plasticity
Shuji KAWAI, Hideki ISHIDA, Yasuo SHIBASAKI, Kiichi ODA
1999 Volume 107 Issue 1251 Pages
1050-1054
Published: November 01, 1999
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Plasticity of ceramic dough is determined by the deformation of the buffer domain that consists of aggregate or gel. Effect of the deformability of each buffer domain on the plasticity of alumina dough, in presence of various additives, was investigated. Those additives were konjak, agar, curdlan and super-absorbent polymer. Moderately deformable additives such as konjak and agar worked as buffer domains, and plasticity was generated. However, soft and brittle additives such as curdlan and super-absorbent polymer could not improve plasticity because of their lower ability in generating the buffer domains. It was clarified that the deformability of buffer domain directly influences plasticity.
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Kenji KAWASAKI, Yoshiharu OZAKI
1999 Volume 107 Issue 1251 Pages
1055-1062
Published: November 01, 1999
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Effects of anionic surfactants on the dispersion of alkoxide-derived SrTiO
3 particles in water and on the formation of SrTiO
3 ceramic sheets were studied in detail. Five kinds of anionic surfactants were examined. All these surfactants enhanced the dispersion of the SrTiO
3 particles in water. Green sheets were prepared from the SrTiO
3 suspensions in aqueous media to which the surfactants and PVA (poly (vinyl alcohol)) were added. The crack- and deformation-free green sheets were obtained from two kinds of suspensions containing the oily alkylbenzenesulfonate type surfactant (mass ratio: SrTiO
3/PVA/surfactant=100/15/20 and 100/15/25). These green sheets were composed of the particles with diameter less than 1μm. The SrTiO
3 ceramic sheets were obtained by heating the green sheets at 1300°C. Linear shrinkage of the sheets during the heat treatment was 30%. Bulk density of the SrTiO
3 ceramic sheets was 4.97g·cm
-3.
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Junichi TATAMI, Atsushi SAIKI, Kouichi YASUDA, Yohtaro MATSUO
1999 Volume 107 Issue 1251 Pages
1063-1066
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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X-ray topographic images of several refraction planes of single crystal alumina were taken with the reflection Berg-Barret technique of X-ray topography. Linear contrasts were observed in X-ray topographic images of fracture surfaces of single crystal alumina. It was shown that dislocations were produced due to the fracture of single crystal alumina even at the room temperature. The comparison among X-ray topograph images made it clear that there were dislocations with several types of Burgers vector near the fracture surface of single crystal alumina, and about 70% of the dislocations were the basal dislocations. X-ray topography is shown to be a powerful technique for obtaining information about dislocations near by the fracture surface of ceramics.
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Toshiaki FURUSAWA, Toshimitsu YOKOBORI
1999 Volume 107 Issue 1251 Pages
1067-1072
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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An attempt has been made to explain the formation of pores on the finished surface of short-fiber-reinforced composite materials, which is brought about by fiber detachment during cutting. A stress analysis of the deformation and fracture behavior caused by the progress of the cutting edge in the macroscopic region at the interface between the matrix material and the fiber is carried out using an elastoplastic finite-element method. This analysis reveals that stress is concentrated at the interface between the matrix material and the fiber far from the cutting edge as a result of the contact of the cutting edge. It is also revealed that cutting occurs by continuance of the microscopic fracture mechanism involving interfacial fracture between the matrix material and fiber far from the cutting edge. Analysis of the fracture region shows that the pore depth is 0.5 which corresponds to the fiber diameter. This is in relatively good agreement with the experimental value of 0.3. Even before the cutting tool touches the fiber, tensile stress is generated in the fiber and it is likely to produce its fracture.
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Yuzo SHIWA, Hiroshi NAKAO, Takanori WATARI, Yasuo IMAOKA
1999 Volume 107 Issue 1251 Pages
1073-1078
Published: November 01, 1999
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Powder and plastic body properties ground by stamp-mill (SM) or ball-mill (BM) were evaluated in the aim of improving the grinding process of Amakusa pottery-stone. SM powder had relatively large amounts (25-30 mass%) of particles both <1μm and >30μm in size. On the other hand, BM powder had relatively large amount (20-25 mass%) of particles 5-10μm and 10-20μm in size. Very fine particles (<1μm) in the SM powder contained much clay components compared to the BM powder. Shear stress in the BM clay body was larger than that in the SM clay body, when the water content was decreased. Therefore, the SM body had higher fluidity than the BM body. It is supposed that the fluidity of the SM body was high because the friction between particles was low, as a consequence of the small size (<1μm) of the clay minerals. Grinding to larger amounts of fine clay minerals would be useful to reach high plasticity in the green body.
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Hiroyo SEGAWA, Tetsuji YANO, Shuichi SHIBATA, Masayuki YAMANE
1999 Volume 107 Issue 1251 Pages
1079-1086
Published: November 01, 1999
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The validity of separating O1s photoelectron spectra of alkaline phosphate glasses into three peaks assigned to bridging, non-bridging and double-bonded oxygen atoms was discussed on the basis of the molecular orbital calculations by density functional method. Models used for the calculations were lithium metaphosphate chain clusters consisting of 2, 4 and 5 PO
4 units. Two oxygen atoms around a Li
+ ion, non-bridging oxygen and double-bonded oxygen, were structurally indistinguishable, and were considered to be classified into the same terminal atoms. The O1s orbital energies of these terminal oxygen atoms were consistent to each other within 0.4eV. The variation in orbital energies probably results from inhomogeneous broadening caused by the statistically distributed surroundings around PO
4 units. From these results, it was concluded that in O1s photoelectron spectra of phosphate glasses, the separation of the lower binding energy side peak into two bands is not appropriate.
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Toetsu SHISHIDO, Masaoki OKU, Iwami HIGASHI, Shigeru OKADA, Kunio KUDO ...
1999 Volume 107 Issue 1251 Pages
1087-1092
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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A new layer structure compound PrRh
4.8B
2 was obtained by a molten metal flux growth method, using Cu as a flux. This compound belongs to the orthorhombic system with the space group
Fmmm. Lattice parameters were
a=0.9697(4)nm,
b=0.5577(2)nm and
c=2.564(3)nm. The structure of the compound is of a modified CeCo
3B
2-type, which is explained by a stacking model of Pr-B and rhodium layers. X-ray photoelectron spectra were taken under three conditions: (i) surface of fractured in the vacuum of the spectrometer; (ii) surface exposed to air after fracture in the spectrometer; and, (iii) surface fractured in air. The X-ray photoelectron spectroscopic study and electron probe micro-analysis results show that a few monolayers of Cu atoms exist between the crystals of PrRh
4.8B
2. The thermo-gravimetric curve shows that oxidation of the PrRh
4.8B
2 proceeds above 873K. Weight gain of the specimen heated up to 1473K in air is 13.44%. Sample forms PrBO
3 and Rh as a result of the oxidation. The temperature dependence of the inverse static magnetic susceptibility χ
-1 obeys the Curie-Weiss law at temperatures above 50K. The magnetic moment μ
eff is 4.2μ
B and the Curie-Weiss temperature Θ
p is-13K. The value of micro Vickers hardness for
c-plane with the orthorhombic symmetry of PrRh
4.8B
2 is 6.7±0.6GPa.
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Analysis of Compression Behavior
JunIchiro TSUBAKI, Takamasa MORI, Toshiyuki KONISHI, Akihisa TSURUTA, ...
1999 Volume 107 Issue 1251 Pages
1093-1098
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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Mechanical properties of spray-dried alumina granules have been characterized by applying and continuos wearing compression stress, repeatedly. The microstructure of compacts was analysed after each compaction level, in order to identify the main factor governing the compaction mechanism. The compressive stress curves were clearly different from those observed after conventional compression test. It is also shown that the slope of the compressive stress curve strongly depended on dispersant and binder contents. The identification of granules based on the analysis of compression behavior is well correlated to the breaking and/or deforming behavior of granules observed by optical microscopy.
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Toshio KAMIYA, Yoshiteru MAEDA, Kouichi NAKAHATA, Takashi KOMARU, Char ...
1999 Volume 107 Issue 1251 Pages
1099-1104
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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Polycrystalline silicon thin films were fabricated by VHF (100-144MHz) plasma enhanced chemical vapor deposition. Three different source materials were used to grow the films on glass substrates: (1) SiH
2Cl
2/H
2, (2) SiF
4/H
2 and (3) SiH
4/H
2 mixing gases. It was found that the gas mixing ratio where crystal silicon grows strongly depends on the selection of source gas: i.e., crystal growth occurred at mixing ratios (SiF
4/H
2) smaller than 30/10 sccm while the crystal growth in SiH
4/H
2 system required much smaller mixing ratios, such as ≤1/50sccm. Microstructures of the films were also strongly influenced by the source material. (220) orientation structures were easily obtained when SiF
4, SiH
2Cl
2 or B
2H
6 were used, compared to SiH
4. In addition, (400) preferentially oriented film grew on glass when the film was grown at a gas mixing ratio of SiF
4/H
2=30/10sccm and a substrate temperature of 200°C. Chlorinated source gases including SiH
nCl
m (
n+
m=4) are also expected to produce (400) oriented growth.
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Takashi MATSUNO, Kenichi WATANABE, Kenji ONO, Masumi KOISHI
1999 Volume 107 Issue 1251 Pages
1105-1110
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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Preparation and characterization of multilayered ceramics with graded structure of hydroxyapatite (HAP)/partially stabilized zirconia (PSZ) was studied. It was difficult to prepare two-layered bodies only consisting a layer of HAP and a layer of PSZ, because these layers could not bond to each other by conventional sintering procedure. Due to peeling off, it was also difficult to prepare three-layered bodies consisting of a monolithic HAP layer, a layer of HAP and PSZ with weight ratio 1/1, and a PSZ layer. Then, five- and seven-layered HAP/PSZ bodies with graded structure were prepared by atmospheric heating (1450°C, 2h) in an electric furnace. In this case, HAP reacted with PSZ at high temperature, and the resulting product was calcium zirconium oxide (Ca
0.15Zr
0.85O
1.85). Seven- and eight-layered HAP/PSZ bodies with graded structure were also prepared by hot-pressing (1150°C, 1350°C). In this case, the layers bonded very firmly to each other and no peeling off was observed even upon cutting and grinding operations. When the sintering temperature was 1350°C, small cracks parallel to the press direction were generated in the layer of monolithic HAP. The cracks were not detected in any of the remaining layers after sintering at 1150°C. No chemical reaction between HAP and PSZ was found by ordinary XRD analysis in the multilayered body prepared by hot-pressing. The graded structure was confirmed by elemental analytical results of Ca and Zr. The bending strength of the seven-layered HAP/PSZ body was much higher than that of monolithic HAP. The Vickers hardness value of the layer consisting of monolithic HAP was 4.3GPa, increasing with increasing the fraction of PSZ to reach 12.0GPa in the layer of monolithic PSZ.
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Stefano MASCHIO, Sergio BRUCKNER, Giuseppe PEZZOTTI
1999 Volume 107 Issue 1251 Pages
1111-1114
Published: November 01, 1999
Released on J-STAGE: August 06, 2010
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The preparation of zirconia/erbia tetragonal solid solution was attempted by sintering of powders produced by coprecipitation. Calcined powders were attrition milled and green bodies densified to materials having grain size of a nanometer scale. Fired materials reached high density after firing at any temperatures above 1350°C for times of 1h or more; they had a tetragonal structure, provided that the erbia content exceeded 1.5mol%. Materials containing 1.5mol% erbia consisted of both monoclinic and tetragonal phases, when the firing conditions were selected at the lowest temperature for densification (1h at 1350°C). In all other cases, only the monoclinic structure could be detected. Materials containing 2, 2.5 and 3mol% erbia had tetragonal symmetry. In particular, tetragonal solid solutions contaning 2mol% Er
2O
3 mantained such structure until their grain size did not exceed 1μm, at larger grain sizes they transformed to monoclinic. The tetragonal lattice parameters were measured by X-ray diffraction analysis in all the tetragonal materials and they agreed with those previously reported by other authors. The crystallographic
a/c ratio had influence on the grain tranformability: the lower the ratio, the lower the tetragonal/monoclinic transformation ratio.
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Hsiung-Wen HAN, Chi-Yen HUANG, Hok-Shing LIU
1999 Volume 107 Issue 1251 Pages
1115-1117
Published: November 01, 1999
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Vapor deposition products were formed in the cold zone (920-1120°C) during synthesis of SiC from carbonized rice hulls (CRHs) in the reaction zone (1500°C) of a vacuum tube furnace during carbothermal reduction. Crystals of gehlenite (Ca
2Al
2SiO
7) and β-SiC whiskers were identified by X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) to be the major deposits. A minor product, suessite (Fe
3Si), appeared to have catalyzed the growth of gehlenite. The results of this study suggest the feasibility of preparing gehlenite materials by a vapor deposition process.
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Masae NAKAHARA, Yoshihito KONDO, Zenbe-e NAKAGAWA, Kenya HAMANO
1999 Volume 107 Issue 1251 Pages
1118-1121
Published: November 01, 1999
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Cordierite sintered bodies were prepared from the mixtures of raw or calcined materials, which were composed of kaolinite, talc and alumina. As many cracks occurred in sintered bodies prepared from mixture of raw materials, the bodies experienced the low thermal expansion coefficients of 1.06-1.39×10
-6/°C (25-900°C), and the low bending strengths of 50-70MPa. The cracks were caused by the orientation of cordierite crystals during the sintering process, owing to the orientation of kaolinite in the forming process. On the other hand, in bodies sintered from the mixture of calcined materials, there were no cracks, the thermal expansion coefficients were higher, about 2.0×10
-6/°C, and the bending strength was about 120MPa.
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